The present disclosure relates to a light beam expanding device, an optical device in which the light beam expanding device is incorporated, and an image display device in which the optical device is incorporated.
A virtual image display device (image display device) for causing a viewer to view a two-dimensional image formed by an image forming device as a magnified virtual image by a virtual image optical system is well known from e.g. JP-T-2005-521099 and Japanese Patent Laid-open No. 2006-162767.
As shown in a conceptual diagram of FIG. 37, this image display device 1000 includes an image forming device 1011 having plural pixels arranged in a two-dimensional matrix manner, a collimating optical system 1012 that turns light output from the pixels of the image forming device 1011 to collimated light, and a light guide unit 1030 on which the light turned to the collimated light by the collimating optical system 1012 is incident. The incident light is guided and output by the light guide unit 1030. The light guide unit 1030 includes a light guide plate 1031. The incident light is propagated inside the light guide plate 1031 by total reflection and then output therefrom. The light guide unit 1030 also includes a first deflector 1040 (for example, formed of one layer of a light reflective film) that reflects the light incident on the light guide plate 1031 in such a manner that the light incident on the light guide plate 1031 may be totally reflected inside the light guide plate 1031. The light guide unit 1030 further includes a second deflector 1050 (for example, formed of a light reflective multilayer film having a multilayer-stacked structure) that outputs the light propagated inside the light guide plate 1031 by total reflection from the light guide plate 1031. If e.g. a head mounted display (HMD) is configured by such an image display device 1000, reduction in the weight and size of the device can be achieved.
Besides, a virtual image display device (image display device) using a hologram diffraction grating for causing a viewer to view a two-dimensional image formed by an image forming device as a magnified virtual image by a virtual image optical system is well known from e.g. Japanese Patent Laid-open No. 2007-094175 and Japanese Patent Laid-open No. 2007-012530.
As shown in conceptual diagrams of FIG. 38 and FIG. 39, this image display device 1100 basically includes an image forming device 1111 that displays an image, a collimating optical system 1112, and a virtual image optical system (light guide unit 1130) on which light displayed on the image forming device 1111 is incident. The light guide unit 1130 guides the incident light to a pupil 41 of the viewer. The light guide unit 1130 includes a light guide plate 1131 and a first diffraction grating member 1140 and a second diffraction grating member 1150 that are formed of reflective volume hologram diffraction gratings provided on the light guide plate 1131. Light output from the respective pixels of the image forming device 1111 is incident on the collimating optical system 1112 and collimated light is generated by the collimating optical system 1112 to be incident on the light guide plate 1131. The collimated light is incident on a first surface 1132 of the light guide plate 1131 and output therefrom. The first diffraction grating member 1140 and the second diffraction grating member 1150 are attached to a second surface 1133 of the light guide plate 1131 which is in parallel to the first surface 1132 of the light guide plate 1131.